1. The Field of the Invention
The present invention relates to caps for writing instruments which can provide means for permitting air to flow through the cap to thereby eliminate or minimize a potential threat to safety when swallowed.
2. Description of the Prior Art
Caps for writing instruments such as markers and pens which employ water-soluble ink, for example, are designed to have a substantially air-tight seal about the nib or pen-point of the instrument to prevent drying out of the ink. To this end, an attempt has been made to enclose the point or nib in an air-tight condition by using a relatively small sized inner cap element. In this attempt, the small sized inner cap is press-fitted into a relatively large outer casing which constitutes a cap for a writing instrument, and this inner cap provides an air-tight seal about the nib of the writing instrument. U.S. Pat. No. 5,066,156 (corresponding to International Publication WO91/14582 and Japanese Publication No. 5-500932) shows a writing instrument cap which will be explained briefly with reference to FIG. 7. In the known cap structure shown in FIG. 7, the cap includes an outer shell 23 which has a front opening and a rear opening. The cap also includes an integral tip seal member 20 which includes an open front end and a closed rear end and is fixedly positioned in the central region of the outer shell. An open front end of the tip seal member 20 is adopted to retain the end of a writing instrument barrel which carries a point or nib to provide a substantially air-tight seal about the point or nib. The tip seal member 20 is spaced apart from the inner surface of outer the shell 23 by a plurality of ribs 21. The ribs 21 are arranged to extend longitudinally so that the ribs 21 form a plurality of adjacent passageways. Recesses 22 are formed on the ribs 21 so that they can be pushed through flange 24 to engage a top surface of the flange 24 with a snap lock fit. Thus, the tip seal member 20 is locked about the flange 24 by the recess 22 and a top surface of the ribs 21.
The cap disclosed in U.S. Pat. No. 5,066,156, however, has disadvantages in that (1) the outer shell 23 is tapered toward a rear end thereof and the inner cap or tip seal member 20 must be forcibly fit into the outer shell 23 by using a tool such as a pushing rod or the like, resulting in an inefficient assembly of the tip seal member into the outer shell, (2) the recess 22 of the tip seal member 20 and the flange 24 of the outer shell 23 do not provide a sufficiently large deformation and, accordingly, the fixture or coupling of the two elements must be established by a very small frictional engagement, and in some cases, the coupling portions are scraped or struck out by a successive forcible press-fit engagement operation, which results in loose engagement and unexpected disengagement of the inner cap or tip seal member 20 from the outer shell 23, and (3) the tip seal member 20 must provide an air-tight seal with respect to a barrel portion of the nib of the writing instrument and therefore a very accurate positional relation is required which, however, is not fully satisfied by only one engagement portion between the recess 22 and the flange 24 and, therefore, the tip seal member 20 is not fixed to the outer shell 23 with respect to all directional movements.